1. Field of the Invention
The present invention relates generally to a baler and, more particularly, is concerned with an improved linkage for controlling a needle safety latch on the baler.
2. Description of the Prior Art
A conventional baler has a fore-and-aft extending bale case within which a plunger is reciprocably driven by a rotating crank arm through working and return strokes for forming a bale of crop material in the bale case. Crop material is fed into the bale case in successive charges and each charge is compressed by the plunger on its working stroke.
A plurality of charges produce a bale of crop material and when the bale is completed it is banded by a tying medium, such as by strands of twine or wire. The tying medium is extended around the completed bale by movable needles which are projectable across the bale case. Specifically, the needles are moved across the bale case, a tying operation is completed and then the needles are retracted from the bale case, all occurring between the last working stroke of the plunger which completed the bale and the next successive working stroke of the plunger for starting the next bale. Since the needles are moved across the path of travel of the plunger and the charge of crop material being compressed by the plunger, precise synchronization or timing is required between the continuous reciprocation of the plunger and the movement of the needles.
It sometimes happens that the drive mechanism for moving the needles breaks at a time when the needles are projected across the bale case. Instead of being retracted, they are left in the bale case and in the path of the plunger on its next working stroke and thus in the path of the next charge of crop material being carried and compressed by the plunger.
To prevent damage to the needles which would otherwise result under such circumstances, it is common practice to provide a safety latch to stop the plunger on its next working stroke. Conventionally, such latch is mounted on the bale case and extendible into the reciprocatory path of the plunger or the rotational path of the rotating crank arm which drives the plunger. The latch is moved to its extended position each time the needles are moved through the bale case and to a retracted position when the needles are withdrawn from the bale case. Thus, if the needles are in the bale case when the plunger moves on a working stroke, the plunger or the crank arm, depending upon the particular arrangement being provided, will engage the safety latch, causing the plunger to stop. To prevent the drive mechanism to which the crank arm is attached from being damaged, one or more shear bolts are provided which break when the latch stops the movement of the plunger.
However, during those periods of normal operation of the baler when the drive mechanism for the needles is functioning properly to move the needles into and out of the bale case in precise synchronization with the reciprocating strokes of the plunger, it is essential that the needle safety latch be completely withdrawn to its retracted position after each extension thereof each time the needles have been fully retracted from the bale case in order that the reciprocation of the plunger on its next working stroke will not be inadvertently disrupted.
Heretofore, the safety latch has commonly been spring-biased to move toward its extended position, with several types of linkages being found in the prior art for allowing the latch to move to its extended position when the needles are projected through the bale case and for retracting the latch when the needles are withdrawn from the bale case.
One type of prior art linkage, being disclosed in U.S. Pat. Nos. 2,868,114, 2,882,813 and 3,027,825, interconnects the mechanism being associated with the safety latch and a lever being pivotally mounted on the bale case adjacent a swingable yoke which mounts the needles. As the yoke reaches its home or rest position in retracting the needles from the bale case, it strikes and pivots the lever which causes retraction of the safety latch.
In a second type of prior art linkage, as disclosed in U.S. Pat. No. 2,957,407, a fore-and-aft extending link arm is disposed adjacent the needle yoke and connected with the mechanism of the safety latch. Again, as the yoke returns to its home position in retracting the needles, a roller carried by the yoke strikes an abutment on the link arm and causes the link arm to move so as to retract the latch.
A third type of prior art linkage provides a flexible cable which interconnects the needle yoke and a pivotal crank mounted on the bale case and connected to the mechanism of the safety latch. As the yoke is moved so as to project the needles through the bale case, the cable slackens allowing the latch to move to its extended position. However, as the yoke returns to its home position in retracting the needles from the bale case, the cable is suddenly drawn taut and pivots the crank arm so as to cause retraction of the safety latch.
While all of the above-described prior art linkages would appear to be satisfactory if properly adjusted, they all are apt to need adjustment or repair after extended periods of normal use of the baler due to the sudden shock or impact loads imparted on the parts thereof when engaged or moved by the moving needle yoke. Such loads frequently result in wear and material fatigue or failure of the parts. Also, in the case of those linkages incorporating flexible cables, the rapid movement of the yoke to its home position causes a whipping of the cable as the slack therein is suddenly taken up. Such whipping action after a period of use stretches the cable and, consequently, the safety latch will not then be fully retracted unless the length of the cable is adjusted to shorten it.